Five Jamaican athletes, including Asafa Powell, have tested positive for banned performance-enhancing drugs, according to the country's anti-doping authority.

Herb Elliott, chairman of the Jamaican Anti-Doping Commission (JADCO), confirmed the body had received "reports of adverse analytical findings from 'A' samples."

He said: "The process of the result management has commenced in accordance with the JADCO anti-doping rules.

"We cannot disclose any further information until the athletes have responded to notification of the 'A' sample."

Image:Sherone Simpson won a silver medal at London 2012

Sprinter Asafa Powell was revealed to be one of the athletes after his management company confirmed he had failed a drugs test.

And Olympic relay silver medallist Sherone Simpson also admitted she had tested positive for a stimulant after last month's national championship.

Powell's agent Paul Doyle confirmed the former 100m world record holder had tested positive for a banned substance.

The 30-year-old has won gold medals in the 4x100m relay at the Olympics and World Championships and is a former world record holder.

In a statement, Powell said: "I can confirm that a sample I gave at the national trials in June last year this year has returned 'adverse findings'.

"The substance oxilofrine (methylsynephrine) was found, which is considered by the authorities to be a banned stimulant.

"I want to be clear in saying to my family, friends, and most of all my fans worldwide that I have never knowingly or willfully taken any supplements or substances that break any rules.

Image:Tyson Gay revealed he had tested positive for an unknown substance

"I am not now - nor have I ever been - a cheat."

Simpson, 28, was a member of the Jamaica team that finished second in the 4x100m relay at London 2012.

In a statement, she said: "This is a very difficult time for me.

"I was notified on July 14, 2013, that my urine sample taken at the National Senior Championship, June 21, 2013, after the 100m finals returned a positive analytical finding for a stimulant, oxilofrine (methylsynephrine).

"As an athlete, I know I am responsible for whatever goes into my body. I would not intentionally take an illegal substance of any form into my system."

Last month, Jamaica's most successful female athlete Veronica Campbell-Brown tested positive for a diuretic, which can be used to mask the use of performancing-enhancing drugs.

The twice Olympic 200 metres champion has been suspended by the Jamaican Athletics Administrative Association pending the outcome of a disciplinary panel hearing.

It comes after former double sprint world champion Tyson Gay announced on Sunday that he had tested positive for a substance he could not identify and was withdrawing from next month's world championships in Moscow.

The American, who had the year's fastest 100 metre time of 9.75 seconds, said he was notified by the US Anti-Doping Agency on Friday that his A sample from an out-of-competition test on May 16 had returned a positive.

He said: "I don't have a sabotage story. I don't have lies ... I basically put my trust in someone and I was let down.